1. Technical Field
The present invention relates to a light source device, a lighting device, a monitor device, and a projector, and in particular to a technology of a light source device for supplying a laser beam.
2. Related Art
In recent years, as a light source device for a monitor device or a projector, a technology for using a laser source for supplying a laser beam has been proposed. In comparison with a UHP lamp, which has been used as a light source of a monitor or a projector in the past, the laser source device using a laser source has advantages such as high color reproducibility, instant-lighting capability, and long life. As the light source device using the laser source, besides the device for directly supplying the fundamental laser beam from the laser source, a device for converting the wavelength of the fundamental laser beam and then supplying the laser beam with the converted wavelength is known. As a wavelength conversion element for converting the wavelength of the fundamental laser beam, for example, a second harmonic generation/generating (SHG) element has been used. By using the wavelength conversion element, it becomes possible to supply a laser beam with a desired wavelength using an easily available multipurpose laser source. Further, a configuration capable of supplying a laser beam with sufficient intensity can also be provided. Regarding the SHG element, it is known that in the case in which the refractive index distribution is varied by the temperature variation, the phase matching condition is broken, and the efficiency of converting the wavelength is deteriorated. In order for supplying a laser beam with stable intensity with high efficiency, it is desirable to reduce the temperature variation of the wavelength conversion element. For example, in the technology proposed in JP-A-5-198870 (hereinafter referred to as a Document 1), the wavelength conversion element is attached to a substrate having thermal conductivity, and temperature control of the substrate is performed based on the temperature measured by a thermistor disposed in the substrate.
As a factor for varying the temperature of the wavelength conversion element, there can be cited a variation in the amount of absorption of the laser beam to the wavelength conversion element caused by a variation in the laser output, a variation in the ambient temperature of the light source device, and so on. In order for controlling the temperature of the wavelength conversion element with good accuracy even in the condition with such factors, it is desirable to detect the temperature close to the temperature of the wavelength conversion element itself. In this respect, in the configuration proposed in the Document 1 described above, the substrate with a volume several times as large as the wavelength conversion element is shown. Since such a big substrate has a large heat capacity, when a factor for causing the temperature of the wavelength conversion element to vary occurs, a large temperature difference should be caused between the wavelength conversion element and the substrate. Therefore, even if the thermistor disposed in such a substrate is used, there arises a problem that it is sometimes difficult to control the temperature of the wavelength conversion element with good accuracy.